2018 Forgash Scholar

Sergiu Dragata

Sergiu Draguta

Spatially-resolved charge carrier transport measurements in high efficient perovskite solar cells

Department of Chemistry and Biochemistry
Faculty Advisor: Masaru (Ken) Kuno

Hybrid perovskites (MAPbI3) represent a potential paradigm shift for creating low-cost solar cells. Despite power conversion efficiencies (PCEs) that now exceed 22%, record PCEs are still far from their theoretical Shockley-Queisser limit of 31%. To further increase PCEs a better understanding of microscopic insight into solar cell performance beyond simple device-level metrics such as open circuit voltages (Voc), short circuit currents (Jsc), fill factors (FFs) and PCEs. Previously, we measured for the first time, spatially-resolved trap densities, photocurrent, quasi-fermi level splitting and PCEs in working hybrid perovskite devices. However, understanding the transport properties on local PCE in hybrid perovskite solar cell can further improve their efficiency. We therefore propose to address this open question by conducting local carrier time of flight (TOF) measurements to establish spatially-resolved electron and hole mobilities. In this way, we will provide direct electron and hole mobility estimates as well as assess contributions from lateral carrier diffusion to observed photocurrent heterogeneities via appropriate drift/diffusion modeling. Local TOF measurements may also potentially yield more insight into the identity carrier traps since grain boundary-related traps may adversely impact both electron and hole mobilities, leading to spatial correlations between them as well as with Nt. Through appropriate modeling, it may also be possible to estimate relevant trap depths and possible trap distributions in energy. This results along with our previous understanding will provide unprecedented look into the working mechanism of these devices.